The present invention relates to diagnostic monitoring systems and, more particularly, to a portable diagnostic monitoring system for assessing cardiovascular hemodynamic state during the setting of a normal or abnormal heart rhythm. Advantageously, the monitoring system is capable of detecting abnormalities of blood pressure and/or flow.
Changes in cardiac output or blood pressure may be of value in diagnosis and management chronic and/or recurring disease states (e.g., congestive heart failure, hypertension, syncope). Currently, such measurements require invasive intravascular catheters with attached sensors (e.g., pressure, oxygen saturation) or an intra-arterial cannula.
Devices employing the technique of impedance plethysmography (commonly known as Impedance Cardiographs (ICG) when applied to the thorax) have been developed which are external to the body and can provide a surrogate marker of pulsatile blood volume changes and/or surrogate measure of blood flow by detection of changes in bioelectrical impedance (BEI). Typically, these devices use band or spot electrodes around the ends of the thorax and measure change in chest impedance due to altered vascular volumes corresponding to cardiac activity. Current is transmitted through the chest and seeks the path of least resistance, i.e., the blood filled aorta. With each heartbeat, the blood volume and velocity of the aorta change. Impedance plethysmography measures the corresponding change in impedance and calculates the hemodynamic parameters.